WWI is frequently described as a long-fused inevitable conflict, yet this comprehensively researched, gracefully written account of the war’s genesis convincingly posits a bad brew of diplomatic contingencies and individual agency as the cause. Clark, history professor at Cambridge University, begins by describing the interactions of Serbia and Austria-Hungary, which sparked the conflict. He presents the former as a “raw and fragile democracy” whose “turbulent” politics challenged a neighboring empire held together by habit. Indeed, the instability across Europe further polarized alliance networks—foreign policies were shaped by “ambiguous relationships... and adversarial competitions” that obfuscated intentions. Nevertheless, the European system demonstrated “a surprising capacity for crisis management.” But even the détente years of 1912–1914 were characterized by “persistent uncertainty in all quarters about the intentions of friends and potential foes alike.” Beginning with the assassination of Archduke Franz Ferdinand, that uncertainty informed the burgeoning crisis—Austria-Hungary’s hesitation allowed Russia to frame the event as a tyrant “cut down by citizens of his own country”; Britain and France offered no challenge to the narrative; and Germany “counted on the localization of the Austro-Serbian conflict.” Instead Russia escalated the crisis by mobilizing, Britain by hesitating, and Germany by panicking: Europe sleepwalked into “a tragedy.” B&w illus., 7 maps. Agent: Andrew Wylie, the Wylie Agency. (Apr.)